Abstract: Giant planet formation process is still not completely understood. Thecurrent most accepted paradigm, the core instability model, explains severalobserved properties of the solar system-s giant planets but, to date, has faceddifficulties to account for a formation time shorter than the observationalestimates of protoplanetary disks- lifetimes, especially for the cases ofUranus and Neptune. In the context of this model, and considering a recentlyproposed primordial solar system orbital structure, we performed numericalcalculations of giant planet formation. Our results show that if accretedplanetesimals follow a size distribution in which most of the mass lies in30-100 meter sized bodies, Jupiter, Saturn, Uranus and Neptune may have formedaccording to the nucleated instability scenario. The formation of each planetoccurs within the time constraints and they end up with core masses in goodagreement with present estimations.